In a wireless communication system, such as 3rd generation (3G) wireless code-division multiple access (CDMA) system, is desired to concurrently support multiple services and multiple data rates for multiple users in a fixed bandwidth channel. One scheme uses adaptive modulation and coding (AMC) to modulate and encode user data symbols before transmission.
In order to increase the capacity of a wireless communication system in fading channel environments, transmit diversity is widely adopted. In 3G systems, an open loop solution uses two antennas for transmission and a single antenna for reception. In such a system, every two symbols of the transmitted data is further encoded by a space-time transmit diversity (STTD) encoder to generate four encoded symbols, two symbols for each antenna. Each antenna transmits different symbol streams through the channel to reach diversity gains.
To support real-time multimedia services in a fixed channel bandwidth, multiple input/multiple output (MIMO) systems have been developed for high data rate transmissions in wireless communication systems, such as high speed downlink packet access (HSDPA) in WCDMA systems. In a MIMO system, multiple antennas are used by the transmitter and the receiver to increase the capacity of the system.
In general, the system capacity is improved as the dimension of the diversity, i.e., number of the antennas, increases. For very high speed transmission, a large number of antennas might be necessary to reach the target performances. One solution to this problem is to extend the current STTD system to MIMO configurations. In such a system, the compatibility with the current STTD system needs to be remained in order to use current STTD system for lower data rate transmission, such as voice services, while the system capacity is improved due to the use of MIMO configurations.